We used a prospective case-cohort design to determine whether total homocysteine (tHcy)-related factors are associated with incidence of coronary heart disease (CHD) over an average of 3.3 years of follow-up in a biracial sample of middle-aged men and women. Age-, race-, and field center-adjusted CHD incidence was associated positively (P<0.05) with tHcy in women but not men, and CHD was associated negatively (P<0.05) with plasma folate (women only), plasma pyridoxal 5=-phosphate (both sexes), and vitamin supplementation (women only). However, after accounting for other risk factors, only plasma pyridoxal 5=-phosphate was associated with CHD incidence; the relative risk for the highest versus lowest quintile of pyridoxal 5=-phosphate was 0.28 (95% CI=0.1 to 0.7). There was no association of CHD with the C677 T mutation of the methylenetetrahydrofolate reductase gene or with three mutations of the cystathionine ?-synthase gene. Our prospective findings add uncertainty to conclusions derived mostly from cross-sectional studies that tHcy is a major, independent, causative risk factor for CHD. Our findings point more strongly to the possibility that vitamin B6 offers independent protection. Randomized trials, some of which are under way, are needed to better clarify the interrelationships of tHcy, B vitamins, and cardiovascular disease. FUNDING Collaboration with Dr. Aaron Folsom, University of Minnesota PUBLICATIONS Folsom AR, Nieto FJ, McGovern PG, McGovern PG, Tsai MY, Malinow MR, Eckfeldt JH, Hess DL, Davis CE. Prospective study of coronary heart disease incidence in relation to fasting total homocysteine, related genetic polymorphisms, and B vitamins The Atherosclerosis Risk in Communities (ARIC) Study. Circulation 98:204-210, 1998.